The paper industry's demand for high white paper products is increasing. This requires usage of well bleached fibers and high dosage offluorescent brightening agents(FBA) often applied both in the wet and at the size press. The dosing level of FBAs at both processes is quite often near the saturation point. Specialty paper makers may also use fluorescent colorants for shaded grades, in combination with non-fluorescent colorants and sometimes FBAs. Thus there is an immen=diate need for reliable, repeatable, and reproducible measurement of colour in fluorescent grades. The paper industry uses a variety ofspectrophotometers and colorimeters as their laboratory quality reference instruments. Unfortunately, even on non-fluorescent grades the agreement between different color instrments is not at the level provided by measurements of properties such as weight or caliper. Furthermore, laboratory instruments measure a stack of sheets, while on-machine instruments measure a single layer, causing additional sources of instrument disagreement and quality deviations.
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